Ductless systems such as Fujitsu’s are a common way to heat and cool Marin homes that never had ducts, from hillside houses in Larkspur to waterfront homes in Sausalito. They are quiet, efficient inverter heat pumps, and they ask for a slightly different kind of diagnosis than a furnace and AC: the system watches several temperature sensors, adjusts its own speed, and stops with a fault code when something is out of range. Most Fujitsu repairs come down to three things: sensors, refrigerant leaks, and airflow lost to dirt.
Single-zone or multi-zone
A single-zone system pairs one indoor unit with one outdoor unit. When it fails, the fault is in that pair.
A multi-zone system runs several indoor units, often one per room, from a single outdoor unit. That changes the first question we ask: is the whole system down, or just one room? If every room has stopped, the outdoor unit, its power or its compressor drive is the suspect. If one room is out while the others run, the cause is usually that room’s indoor unit, its sensors, its line set or the electronic valve feeding it. Some multi-zone problems are wiring problems: indoor units connected to the wrong ports, or communication wires swapped, can make one room respond to another room’s remote.
Sensors: when the unit reads the room wrong
A Fujitsu system relies on thermistors, small temperature sensors, in the indoor unit (room air and coil) and the outdoor unit (outdoor air, coil and compressor discharge). A sensor that drifts or fails can:
- shut the unit down with a code;
- make it stop short of the setpoint, or overshoot it;
- confuse the defrost cycle so the outdoor coil ices up in heating mode.
We test each sensor’s resistance against its temperature chart and check the connector on the board before replacing anything; a corroded or loose plug causes the same symptoms as a failed sensor.
Refrigerant leaks
Fujitsu systems are sealed, and they lose refrigerant only through a leak. The usual places are the flare joints at the indoor and outdoor units, a line set kinked or rubbed through during installation, and, less often, a coil. A slow leak shows up as weaker cooling and heating over months, an indoor coil that frosts, or the outdoor unit running long without reaching the setpoint. We find the leak, repair it, pull a deep vacuum and weigh in the correct charge, rather than topping it off. Our refrigerant leak page lists the warning signs.
Filters, coils and airflow
The washable filters in a wall-mounted head clog quickly, and the coil and blower wheel behind them collect dust and, in damp rooms, mold. The result is weak airflow, a musty smell, water dripping from the head and higher power use. A proper cleaning removes the blower wheel or cleans it in place, washes the coil and flushes the drain. On ducted Fujitsu units, obstructed filters and ductwork cause the same airflow loss. See ductless mini-split service for what a cleaning visit includes.
Our approach
We are independent and not affiliated with Fujitsu. You get an itemized price after the diagnosis. Parts are factory certified and carry the manufacturer’s warranty, and our work carries a labor warranty. Same-day service is usually possible when you call before noon.
Local notes
In Sausalito, outdoor units on decks and houseboats sit in salt air, which corrodes coil fins, electrical connections and mounting brackets faster than inland. A yearly check, a fresh-water rinse of the outdoor coil and a look at the line set insulation help a Fujitsu system last. On steep Larkspur lots, outdoor units are often in tight spots where leaves and debris collect against the coil, so clear the area around them in fall.